The Upper Permian Changxing dolomite reservoirs serves as one of the most important gas and oil reservoirs in the NE Sichuan Basin. Determining the dolomitizing fluid＇s pathway is regarded as the key to solve the ＂d...The Upper Permian Changxing dolomite reservoirs serves as one of the most important gas and oil reservoirs in the NE Sichuan Basin. Determining the dolomitizing fluid＇s pathway is regarded as the key to solve the ＂dolomite problem＂ and further petroleum exploration. Outcrop samples from Upper Permian Changhsingian Panlongdong Section were studied using oxygen isotopic analysis, cathodoluminescence（CL） and major element analysis, in an attempt to determine the migration path way and properties of the dolomitizing fluid. Of the Changxing dolomite, the δ18O values ranged from-3.494‰ to-5.481‰, which decreased from the top layer to the bottom in the section; the MgO contents varied from 9.24% to 21.43%, CaO contents from 28.65% to 39.87%, the CaO/MgO ratio from 1.40 to 4.31 and the Mn O contents from 0.004% to 0.009 8%. The Mg O contents showed a downwardly decreasing trend in the section, while the Ca O/Mg O showed an opposite rule. All of the dolomites looked dull or dark when they were exposed to the electron beam of the cathodoluminescence device. None of the fine-to medium grained dolomite showed a banded structure. Given that dolomitizing fluid＇s salinity decreased during the dolomitization process in its pathway, we concluded that the dolomitizing fluid migrated downwardly in Changxing Formation after excluding the possibility of deep burial or meteoric-marine mixing-water influences. As the dolomitizing fluid＇s pathway has always been difficult to be determined in highly dolomitized Formation, this study showed an important application of oxygen isotope values in resolving this problem.展开更多
Lacustrine dolomite is paid increasing attention to uncover the diagenetic water condition of paleo-lake and“dolomite problem”.Here,a dolomite nodule from the Qingshankou Formation in the Songliao Basin was analyzed...Lacustrine dolomite is paid increasing attention to uncover the diagenetic water condition of paleo-lake and“dolomite problem”.Here,a dolomite nodule from the Qingshankou Formation in the Songliao Basin was analyzed to explore the salinity,alkalinity,and redox conditions of the diagenetic water.Multiple proxies,including bulk boron(B)content,B isotope composition(δ^(11)B_(bul)),boron to gallium weight ratio(B/Ga)and carbonate oxygen isotope composition(δ^(18)O_(carb)),were used to determine the diagenetic water to be brackish-fresh.Through numerical simulation,we calculated the B contents,δ^(11)B values and B/Ga in detritus(e.g.,clay,quartz and feldspar)and dolomite as two endmembers,confirming the intense interference of clay minerals onδ^(11)B_(bul).By using the fittedδ^(11)B of dolomite endmember(20.6‰),we calculated the p H value of the diagenetic water to be 8.2.The negativeδ^(11)B value of detritus endmember(-12.9‰)might be related to the terrestrial weathering.The indicative nature of strontium to barium weight ratio(Sr/Ba)was discussed to deny its applicability as a proxy of salinity in carbonate system.High Sr/Ba ratio in this dolomite nodule indicates a sulfate-poor water condition,consistent with the iron-manganese(Fe-Mn)reduction environments reflected by the Mn/Fe molar ratio.The positive carbonate carbon isotopes(δ^(13)C_(carb),4.5‰-9.4‰)indicate that methanogenesis dominated the formation of dolomite,coinciding with the weak sulfate reduction reaction in sulfate-poor water.The growth of dolomite nodule might be related to the microbial activities of methanogen and iron reducing bacteria,which had not only maintained the salinity,p H,and redox status of the diagenetic water,but also led to a ferricmethane transition zone(FMTZ).This research depicts a scenario about the diagenetic water environment of lacustrine dolomite formed in brackish-fresh water,which is different from that occurred in sulfate-rich condition.展开更多
Surface pretreatment can change the surface properties of minerals,placing them in either a favorable or an unfavorable state for flotation.To solve the separation problem associated with magnesite and dolomite,surfac...Surface pretreatment can change the surface properties of minerals,placing them in either a favorable or an unfavorable state for flotation.To solve the separation problem associated with magnesite and dolomite,surface pretreatment experiments with citric acid,tartaric acid,and tannic acid(TA)on magnesite and dolomite as well as flotation experiments on pretreated samples were performed in this study.Experimental results demonstrated that when citric acid and tartaric acid are used for surface pretreatment,the separation effect of magnesite and dolomite is poor.However,when TA is used,the separation effect of magnesite and dolomite improves.SEM and BET analysis indicated that surface pretreatment with TA changes the surface morphology of the two minerals,resulting in additional concave pores on the dolomite surface,and a significant increase in pore size and specific surface area.The adsorption quantity test and contact angle measurement demonstrated that after surface pretreatment with TA,the magnesite adsorption capacity on sodium oleate(NaOL)slightly decreases and the dolomite adsorption capacity on NaOL considerably decreases.XPS detection concluded that the surface pretreatment of TA on the magnesite surface mainly relies on physical adsorption with weak adsorption ability and poor ability to act on Mg sites.The TA surface pretreatment action on the dolomite surface is mainly through chemical adsorption,and it is strongly and selectively adsorbed on the Ca site of dolomite through O.Actual ore rough selection experiments reveal that TA pretreatment successfully removes dolomite from magnesite,resulting in a high-quality magnesite concentrate characterized by a MgO grade of 45.49%and a CaO grade of 0.75%.展开更多
The effect of depositional facies and diagenesis on the reservoir potential of the Sakesar limestone has been assessed through core plug porosity and permeability data,scanning electron microscope(SEM),and petrographi...The effect of depositional facies and diagenesis on the reservoir potential of the Sakesar limestone has been assessed through core plug porosity and permeability data,scanning electron microscope(SEM),and petrographic study in three stratigraphic sections(Karuli,Badshah Pur,and Sardhai)of Central Salt Range.Field observations reveal three lithofacies:thin-bedded limestone with shale intercalation,thick-bedded nodular limestone,and highly fractured limestone.Based on a petrographic study,six microfacies have been identified:bioclastic mudstone facies(SKF-1),Lockhartia-nummulitic wackestone facies(SKF-2),Assilina-Alveolina packstone facies(SKF-3),Lockhartia-nummulitic packstone facies(SKF-4),Alveolina grainstone facies(SKF-5),and nummulitic grainstone facies(SKF-6).The Sakesar limestone shows various diagenetic changes such as compaction,dissolution,dolomitization,cementation,and fracturing,resulting in different types of pores.Two reservoir zones are identified in the Sakesar limestone:a mud-dominated reservoir in an outer ramp setting with interparticle and micropores and a bioclastic grain-dominated facies in an inner ramp setting with intraskeletal and fracture porosity.The porosity and permeability of grain-dominated facies(8%-30%and 0.8-8 mD)are higher than mud-dominated facies(4%-15%and 0.5-4 mD)due to intraskeletal/intraparticle pores and dolomitization.展开更多
To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings rev...To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content.The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages:accelerated,decelerated,and stabilized stages.During this process,the number of pores in dolomite increases,while the pore diameter initially decreases and then fluctuates.Microscopic analysis shows that the proportion of mesopores first increases and then decreases,while micropores exhibit the opposite trend,and the proportion of macropores fluctuates around 0%.A model diagram of structural evolution during water absorption has been developed.Additionally,the softening process of dolomite’s water absorption strength is categorized into three stages:a relatively stable stage,an accelerated softening stage dominated by mesopore water absorption,and a decelerated softening stage characterized by micropore water absorption.A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion,and experimental validation indicates its strong applicability.展开更多
The widespread dolomite of the Sinian Dengying Formation in the Sichuan Basin(China)serves as one of the most important oil and gas reservoir rocks of the basin.Well WT1,as an exploration well,is recently drilled in t...The widespread dolomite of the Sinian Dengying Formation in the Sichuan Basin(China)serves as one of the most important oil and gas reservoir rocks of the basin.Well WT1,as an exploration well,is recently drilled in the Kaijiang County,northeastern Sichuan Basin(SW China),and it drills through the Dengying Formation dolomite at the depth interval of 7500–7580 m.In this study,samples are systematically collected from the cores of that interval,followed by new analyses of carbon-oxygen isotope,major elements,trace elements,rare earth elements(REEs)and EP-MA.The Dengying Formation dolomites of Well WT1 haveδ13C values of 0.37‰to 2.91‰andδ18O values of-5.72‰to-2.73‰,indicating that the dolomitization fluid is derived from contemporary seawater in the near-surface environment,rather than the burial environment.Based on the REE patterns of EPMA-based in-situ data,we recognized the seawater-sourced components,the mixedsourced components and the terrigenous-sourced components,indicating the marine origin of the dolomite with detrital contamination and diagenetic alteration.Moreover,high Al,Th,and Zr contents indicate significant detrital contamination derived from clay and quartz minerals,and high Sr/Ba and Sr/Cu ratios imply a relatively dry depositional environment with extremely high seawater salinity,intensive evaporation,and strong influences of terrigenous sediment.展开更多
Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tu...Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tunnel of the Yunnan Dianzhong Water Diversion Project,using a combined experimental and modeling approach for systematic analysis.Triaxial cyclic loading-unloading tests were first conducted on dolomite samples soaked in sulfuric acid solutions of varying concentrations,with synchronous monitoring of their mechanical responses(e.g.,peak strength,deformation modulus,porosity changes).These tests,combined with observations of macroscopic morphology and mass changes during soaking,revealed a four-stage degradation pattern of dolomite in sulfuric acid:water absorption,dynamic equilibrium,dissolution,and stabilization.Key quantitative relationships established that as sulfuric acid concentration increased(from 0%to 15%),the peak strength of dolomite decreased significantly(by 7.49%to 24.99%),while porosity markedly increased(by 45%to 130%).Further post-failure analysis(fracture surface observation)and scanning electron microscopy(SEM)micro-characterization uncovered the intrinsic mechanisms of acid-induced damage:the acid solution not only promoted macroscopic crack propagation and increased fracture surface roughness but also triggered severe structural deterioration at the microscale,including enlarged crystal spacing,dissolution of gel-like substances,formation of intra-crystalline pores,weakened interparticle cementation,and development of macropores.The extent of this deterioration was positively correlated with acid concentration.Based on the experimentally revealed chemo-mechanical coupling damage mechanism between acid and rock,this study established,for the first time,a multi-scale predictive model capable of quantitatively correlating acid concentration,microstructural deterioration,and degradation of macroscopic mechanical properties.The development of this model not only deepens the quantitative understanding of the dolomite sanding mechanism but also provides a crucial theoretical tool for assessing surrounding rock stability and predicting risks in similar water diversion tunnel engineering.Addressing the specific risks of water and H^(+) erosion in the Xiaopu Tunnel,the research findings directly informed the engineering reinforcement strategy:concrete lining is recommended as the primary load-bearing structure,supplemented by surrounding rock surface protection measures,to effectively mitigate the acid-induced damage process and enhance the long-term stability of the surrounding rock.展开更多
The dominant lithofacies of reservoirs in the Barra Velha formation of the study area are grainstones,which exhibit strong heterogeneity,and the seismic responses of buildups are characterized by low relief,posing a s...The dominant lithofacies of reservoirs in the Barra Velha formation of the study area are grainstones,which exhibit strong heterogeneity,and the seismic responses of buildups are characterized by low relief,posing a substantial challenge in evaluating the factors controlling high-quality reservoir development.This study thoroughly investigated sedimentary facies and diagenetic processes based on petrological and geophysical data,and a semi-open-rimmed carbonate platform model was established to illustrate the lithofacies distribution pattern.Additionally,the diagenetic processes and their main controlling factors were analyzed,and an attempt was made to establish a diagenetic sequence.Our findings indicate that sedimentary processes control the distribution of lithofacies,while diagenesis ultimately determines the petrophysical properties.The lithofacies types are closely associated with depositional environments.Shrub-like stromatolites are more developed at the bench margin and inner slope,while spherulites occur preferentially in the bench interior and mid-slope environments.Laminites accumulate in profundal or bench interior facies,whereas grainstones are present across all depositional environments,although their components vary.Integrated seismic attributes revealed that the bench margin exhibits nearly circular features,representing favorable conditions for high-quality reservoir development.The primary diagenetic processes in the study area include meteoric diagenesis,chemical compaction,and possible hydrothermal activity.During the eodiagenetic phase,the dissolution of Mg-clays played a key role in the diagenesis of carbonate rocks in the Barra Velha formation.This process typically occurred at structural highs,where Mg-clays were replaced by calcite spherulites,silicates,and dolomite.Some grainstones developed dolomite rims around particles,enhancing their resistance to compaction and preserving primary porosity.In the mesodiagenetic phase,chemical compaction and hydrothermal activity often caused primary pores to be filled with mosaic or blocky calcite and macrocrystalline quartz,leading to reduced permeability and porosity.Although dissolution was common in the study area,its impact on increasing pore space was limited.This study aims to improve drilling success rates in high-quality reservoirs and enhance hydrocarbon discoveries in the study area while also contributing to a better understanding of the evolution and distribution of high-quality reservoirs in analogous lacustrine carbonate settings.展开更多
The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin(NW China)was mainly deposited in a shallow platform,which was intensely bioturbated with burrows filled with both dolomites and calcites.This st...The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin(NW China)was mainly deposited in a shallow platform,which was intensely bioturbated with burrows filled with both dolomites and calcites.This study aims to figure out the controls on the dolomitization of burrow infills and the effects on petroleum reservoir quality based on petrographic examination,fluid inclusion microthermometry,and isotopic(C-O-Sr)geochemical analyses.The differentiation of burrow-associated carbonates(dolomites and calcites)was likely controlled by the interactions of sea-level oscillations of variable orders and depositional environments.The burrow-associated dolomites(BADs)were precipitated in a relatively restricted(i.e.,lagoon)depositional environment during the lowstand of long-term sea level.In contrast,the burrow-associated calcites(BACs)were formed in a water circulation-improved lagoonal environment during the transgression of long-term sea level.Isotopic geochemical data indicate that the BADs in the Yingshan Formation were formed from slightly saline(i.e.,mesosaline to penesaline)seawater,whereas the BACs were precipitated from nearly normal seawater.In addition to the anoxic condition,the presence of marine-sourced organic matter and sulfate-reducing bacteria,and a sufficient supply of dolomitizing fluids enriched in magnesium ions(Mg^(2+))and their Mg^(2+)concentration may have played a critical role in the formation of BADs.In the more permeable and disturbed burrow sediments as a result of burrowing,penetrating fluids with higher salinities and higher Mg^(2+)concentration relative to seawater favored dolomite precipitation.The fluids with seawater-like Mg^(2+)concentration,however,would lead to calcite precipitation.The progressive dolomitization of these burrowed sediments could have propagated the dolomitizing fronts and extended into ambient limestones,leading to the development of extensive dolomites.This dolomitization process can improve the petrophysical properties(porosity and permeability)and the potential as hydrocarbon reservoirs during the emplacement of hydrocarbons from underlying source rocks of the Cambrian to Lower Ordovician.展开更多
The Majiagou Formation in the Fuxian area of the southeastern Ordos Basin has undergone a complex diagenetic evolution history under the influence of eustacy and the Caledonian karstification,resulting in several comp...The Majiagou Formation in the Fuxian area of the southeastern Ordos Basin has undergone a complex diagenetic evolution history under the influence of eustacy and the Caledonian karstification,resulting in several complex reservoir types.Through analyses of mineralogy,petrology,and reservoir geology,three major types of dolomite reservoirs with different genetic mechanisms,including anhydritic moldicdissolved pore type,dolomitic intercrystalline-pore type,and fractured type were identified,and their formation mechanisms and distribution patterns were examined.The aphanocrystalline to very finecrystalline anhydritic dolomite was resulted from Sabhak dolomitization,and is characterized by small size of crystals and high content of anhydrite.Dolomite reservoirs of anhydritic moldic-dissolved pore type were developed in multi-stage dissolution processes and mainly distributed at higher positions of the paleogeomorphology where the filling was weak.The very fine to fine-crystalline dolomite of shoal facies was formed under seepage-reflux dolomitization,and characterized by larger sizes of crystals and well-developed intercrystalline pores.Dolomite reservoirs of intercrystalline-pore type were mainly developed at the lower positions of the paleogeomorphology where bedding-parallel karst dissolution was strong.The fractured dolomite reservoirs,generated by the anhydrite swelling and karst cave collapse,occur in multiple horizons but within limited areas due to multi-stage fillings.展开更多
The origin of dolostone in the Middle Jurassic Buqu Formation of the Plateau Basin has been a subject of prolonged debate.This study combines detailed petrological observations with analyses of Mg-C-O isotopes and ele...The origin of dolostone in the Middle Jurassic Buqu Formation of the Plateau Basin has been a subject of prolonged debate.This study combines detailed petrological observations with analyses of Mg-C-O isotopes and elements to constrain the origin of dolostones in the Buqu Formation.Petrography and cathodoluminescence(CL)examination identified three types of matrix dolostones:very finely to finely crystalline dolostone(D1),finely to medium crystalline dolostone(D2),and medium to coarsely crystalline dolostone(D3).The analysis of the diagenesis sequence reveals that D1 originated from the dolomitization of grainstone in the early diagenetic phase,whereas D2 and D3 resulted from the recrystallization of D1 during the later burial phase.The presence of high Na(>100 ppm),low Fe(<1000 ppm),low Mn(<250 ppm),positive Ce anomaly,LREE enrichment,stableδ^(26)Mg(-2.28‰to-2.04‰),andδ^(13)C(1.02‰-2.95‰)indicates that the early dolomitization fluid was oxidized seawater.As the crystal size increases(D1→D2→D3),the progressively rising Mn content and significantly negativeδ^(18)O(-10.72‰to-7.81‰)suggest that the dolostone has experienced modification and alteration by buried pore water in the later stages.The fluctuations in relative sea level during the sedimentary deposition of the Buqu Formation were reconstructed through the utilization of Na,Sr/Cu,Sr/Ba,Rb/Sr,∑REE,andδ^(13)C.It was observed that theδ^(26)Mg of dolostone closely mirrored the variations in sea level.The consistent trend of change confirms that sea level fluctuations control the formation and distribution of early dolostone.Frequent sea level rise and fall prompted the limestone deposited on the carbonate platform to be continuously transformed into dolostone,which accumulates over a long period to form large-scale thick dolostone.After the formation entered the burial stage,under the combined action of high Mg/Ca ratio pore water,high temperature,and high pressure,the early dolostone experienced the adjustment of burial dolomitization.This research offers a typical case study on the application of Mg-C-O isotope and elements to determine the origin of dolostone.This will aid in a more comprehensive understanding of the formation process of dolostone in ancient rock records.展开更多
This paper discusses the characteristics and formation mechanism of thin dolomite reservoirs in the lower submember of the second member of the Permian Maokou Formation(lower Mao 2 Member)in the Wusheng-Tongnan area o...This paper discusses the characteristics and formation mechanism of thin dolomite reservoirs in the lower submember of the second member of the Permian Maokou Formation(lower Mao 2 Member)in the Wusheng-Tongnan area of the Sichuan Basin,SW China,through comprehensive analysis of geological,geophysical and geochemical data.The reservoir rocks of the lower Mao 2 Member are dominated by porphyritic vuggy dolomite and calcareous dolomite or dolomitic limestone,which have typical karst characteristics of early diagenetic stage.The dolomites at the edge of the karst system and in the fillings have dissolved estuaries,and the dolomite breccia has micrite envelope and rim cement at the edge,indicating that dolomitization is earlier than the early diagenetic karstification.The shoal facies laminated dolomite is primarily formed by the seepage reflux dolomitization of moderate-salinity seawater.The key factors of reservoir formation are the bioclastic shoal deposition superimposed with seepgae reflux dolomitization and the karstification of early diagenetic stage,which are locally reformed by fractures and hydrothermal processes.The development of dolomite vuggy reservoir is closely related to the upward-shallowing sequence,and mainly occurs in the late highstand of the fourth-order cycle.Moreover,the size of dolomite is closely related to formation thickness,and it is concentrated in the formation thickness conversion area,followed by the thinner area.According to the understanding of insufficient accommodation space in the geomorphic highland and the migration of granular shoal to geomorphic lowland in the late highstand of the third-order cycle,it is proposed that the large-scale shoal-controlled dolomite reservoirs are distributed along structural highs and slopes,and the reservoir-forming model with shoal,dolomitization and karstification jointly controlled by the microgeomorphy and sea-level fluctuation in the sedimentary period is established.On this basis,the paleogeomorphology in the lower Mao 2 Member is restored using well-seismic data,and the reservoir distribution is predicted.The prediction results have been verified by the latest results of exploration wells and tests,which provide an important reference for the prediction of thin dolomite reservoirs under similar geological setting.展开更多
Disintegrated dolomite slope and tunnel disasters occur frequently due to poor water stability of disintegrated dolomite,primarily in a form of seepage failure.For engineering purposes,it is critical to determine the ...Disintegrated dolomite slope and tunnel disasters occur frequently due to poor water stability of disintegrated dolomite,primarily in a form of seepage failure.For engineering purposes,it is critical to determine the seepage properties of disintegrated dolomite within the strata.However,conventional experimental methods are time-consuming and expensive and may not be effective in investigating seepage characteristics due to the heterogeneity of disintegrated dolomite.In this study,pore network model(PNM)was established by the computerized tomography(CT)scanning technology to characterize the pores.Meanwhile,the seepage and coefficient of permeability under different inlet stress conditions based on the accurate pore model were realized by linking the commercial image processing software Avizo with the commercial multi-physics modeling package Comsol.The results show that the porosities of severely and completely disintegrated dolomites are 29.17% and 45.37%,respectively.The grade of pore development increases with disintegration grade,which facilitates seepage failure.Severely and completely disintegrated dolomites have the coefficients of permeability of 9.67×10^(-7) m/s and 1.61×10^(-6) m/s,respectively.Under conventional conditions,severely and completely disintegrated dolomites undergo seepage failure above a pressure difference of 6×10^(3) Pa and 5×10^(3) Pa,respectively.These results are consistent with both in situ water pressure tests in the borehole and laboratory tests with the constant-head method,demonstrating that CT scanning is an effective method for observing fractures and pores in disintegrated dolomite for seepage evaluation.展开更多
The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration...The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years.Because of the dolomite-hosted reservoirs in the Feixianguan Formation,these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists.Based on the homogenization temperatures of fluid inclusions,oxygen isotopic composition and their calculated temperatures,and the burial and thermal history of the typical well,it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation,Northeastern Sichuan Basin.Only a minority of dolomites are formed by high-temperature dolomitizing fluids.The ending depth interval of low-temperature dolomitizing fluids was about 1000-2500 m,of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic.The main depth interval of high-temperature dolomitizing fluids was about 3200-4500 m,of which the correspondingly main timing interval was approximately early-middle Middle Jurassic.The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation,Northeastern Sichuan Basin.展开更多
The Ediacaran–Ordovician strata within three major marine basins(Tarim,Sichuan,and Ordos)in China are analyzed.Based on previous studies focusing on the characteristics of the Neoproterozoic–Cambrian strata within t...The Ediacaran–Ordovician strata within three major marine basins(Tarim,Sichuan,and Ordos)in China are analyzed.Based on previous studies focusing on the characteristics of the Neoproterozoic–Cambrian strata within the three major basins(East Siberian,Oman,and Officer in Australia)overseas,the carbonate–evaporite assemblages in the target interval are divided into three types:intercalated carbonate and gypsum salt,interbedded carbonate and gypsum salt,and coexisted carbonate,gypsum salt and clastic rock.Moreover,the concept and definition of the carbonate-evaporite assemblage are clarified.The results indicate that the oil and gas in the carbonate-evaporite assemblage are originated from two types of source rocks:shale and argillaceous carbonate,and confirmed the capability of gypsum salt in the saline environment to drive the source rock hydrocarbon generation.The dolomite reservoirs are classified in two types:gypseous dolomite flat,and grain shoalµbial mound.This study clarifies that the penecontemporaneous or epigenic leaching of atmospheric fresh water mainly controlled the large-scale development of reservoirs.Afterwards,burial dissolution transformed and reworked the reservoirs.The hydrocarbon accumulation in carbonate-evaporite assemblage can be categorized into eight sub-models under three models(sub-evaporite hydrocarbon accumulation,supra-evaporite hydrocarbon accumulation,and inter-evaporite hydrocarbon accumulation).As a result,the Cambrian strata in the Tazhong Uplift North Slope,Maigaiti Slope and Mazatag Front Uplift Zone of the Tarim Basin,the Cambrian strata in the eastern-southern area of the Sichuan Basin,and the inter-evaporite Ma-4 Member of Ordovician in the Ordos Basin,China,are defined as favorable targets for future exploration.展开更多
Flotation separation of magnesite and its calcium-containing carbonate minerals is a difficult problem.Recently,new regulat-ors have been proposed for magnesite flotation decalcification,although traditional regulator...Flotation separation of magnesite and its calcium-containing carbonate minerals is a difficult problem.Recently,new regulat-ors have been proposed for magnesite flotation decalcification,although traditional regulators such as tannin,water glass,sodium carbon-ate,and sodium hexametaphosphate are more widely used in industry.However,they are rarely used as the main regulators in research because they perform poorly in magnesite and dolomite single-mineral flotation tests.Inspired by the limonite presedimentation method and the addition of a regulator to magnesite slurry mixing,we used a tannin pretreatment method for separating magnesite and dolomite.Microflotation experiments confirmed that the tannin pretreatment method selectively and largely reduces the flotation recovery rate of dolomite without affecting the flotation recovery rate of magnesite.Moreover,the contact angles of the tannin-pretreated magnesite and dolomite increased and decreased,respectively,in the presence of NaOl.Zeta potential and Fourier transform infrared analyses showed that the tannin pretreatment method efficiently hinders NaOl adsorption on the dolomite surface but does not affect NaOl adsorption on the magnesite surface.X-ray photoelectron spectroscopy and density functional theory calculations confirmed that tannin interacts more strongly with dolomite than with magnesite.展开更多
Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the control...Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the controlling factors of reservoir development were analyzed,and the formation model of“intra-platform shoal thin-layer dolomite reservoir”was established.The Qixia Formation is a regressive cycle from bottom to top,in which the first member(Qi1 Member)develops low-energy open sea microfacies,and the second member(Qi2 Member)evolves into intra-platform shoal and inter-shoal sea with decreases in sea level.The intra-platform shoal is mainly distributed near the top of two secondary shallowing cycles of the Qi2 Member.The most important reservoir rock of the Qixia Formation is thin-layer fractured-vuggy dolomite,followed by vuggy dolomite.The semi-filled saddle dolomite is common in fracture-vug,and intercrystalline pores and residual dissolution pores combined with fractures to form the effective pore-fracture network.Based on the coupling analysis of sedimentary and diagenesis characteristics,the reservoir formation model of“pre-depositional micro-paleogeomorphology controlling shoal,sedimentary shoal controlling dolomite,penecontemporaneous dolomite benefiting preservation of pores,and late hydrothermal action effectively improving reservoir quality”was systematically established.The“first-order high zone”micro-paleogeomorphology before the deposition of the Qixia Formation controlled the development of large area of intra-platform shoals in Gaoshiti area during the deposition of the Qi2 Member.Shoal facies is the basic condition of early dolomitization,and the distribution range of intra-platform shoal and dolomite reservoir is highly consistent.The grain limestone of shoal facies is transformed by two stages of dolomitization.The penecontemporaneous dolomitization is conducive to the preservation of primary pores and secondary dissolved pores.The burial hydrothermal fluid enters the early dolomite body along the fractures associated with the Emeishan basalt event,makes it recrystallized into medium–coarse crystal dolomite.With the intercrystalline pores and the residual vugs after the hydrothermal dissolution along the fractures,the high-quality intra-platform shoal-type thin-layer dolomite reservoirs are formed.The establishment of this reservoir formation model can provide important theoretical support for the sustainable development of Permian gas reservoirs in the Sichuan Basin.展开更多
To analyze the episodic alteration of Middle Permian carbonate reservoirs by complex hydrothermal fluid in southwestern Sichuan Basin,petrology,geochemistry,fluid inclusion and U-Pb dating researches are conducted.The...To analyze the episodic alteration of Middle Permian carbonate reservoirs by complex hydrothermal fluid in southwestern Sichuan Basin,petrology,geochemistry,fluid inclusion and U-Pb dating researches are conducted.The fractures and vugs of Middle Permian Qixia–Maokou formations are filled with multi-stage medium-coarse saddle dolomites and associated hydrothermal minerals,which indicates that the early limestone/dolomite episodic alteration was caused by the large-scale,high-temperature,deep magnesium-rich brine along flowing channels such as basement faults or associated fractures under the tectonic compression and napping during the Indosinian.The time of magnesium-rich hydrothermal activity was from the Middle Triassic to the Late Triassic.The siliceous and calcite fillings were triggered by hydrothermal alteration in the Middle and Late Yanshanian Movement and Himalayan Movement.Hydrothermal dolomitization is controlled by fault,hydrothermal property,flowing channel and surrounding rock lithology,which occur as equilibrium effect of porosity and permeability.The thick massive grainstone/dolomites were mainly altered by modification such as hydrothermal dolomitization/recrystallization,brecciation and fracture-vugs filling.Early thin-medium packstones were mainly altered by dissolution and infilling of fracturing,bedding dolomitization,dissolution and associated mineral fillings.The dissolved vugs and fractures are the main reservoir space under hydrothermal conditions,and the connection of dissolved vugs and network fractures is favorable for forming high-quality dolomite reservoir.Hydrothermal dolomite reservoirs are developed within a range of 1 km near faults,with a thickness of 30–60 m.Hydrothermal dolomite reservoirs with local connected pore/vugs and fractures have exploration potential.展开更多
Given the depletion of high-quality magnesite deposits and the rising demand for high-end magnesium materials,the separation and utilization of high-calcium magnesite ores have become essential.However,the similar sur...Given the depletion of high-quality magnesite deposits and the rising demand for high-end magnesium materials,the separation and utilization of high-calcium magnesite ores have become essential.However,the similar surface properties and solubility of semi-soluble salt-type minerals,pose significant challenges for the utilization of dolomite-rich magnesite resources.In this study,1-hydroxypropane-1,1-di phosphonic acid(HPDP)was identified for the first time as a high-performance depressant for dolomite.Various tests,including contact angle measurements,ζ potential analysis,X-ray photoelectron spectroscopy,and atomic force microscopy,were conducted to elucidate the interfacial interaction mechanisms of HPDP on the surfaces of the two minerals at different scales.Additionally,molecular modeling calculations were used to detail the spatial matching relationship between HPDP and the crystal faces of the two minerals.It was emphasized that HPDP specifically adsorbed onto the dolomite surface by forming calcium phosphonate,ensuring that the dolomite surface remained hydrophilic and sank.Moreover,it was found that the adsorption strength of HPDP on the mineral surfaces depended on the activity of the metal sites and their spatial distribution.These findings provide a theoretical foundation for the molecular design of flotation reagents for high-calcium magnesite ores.展开更多
With increasingly stringent environmental protection policies,cost-effective and value-added treatment of massive lead-zinc waste rock(LZWR)generated from the preconcentration process has attracted substantial attenti...With increasingly stringent environmental protection policies,cost-effective and value-added treatment of massive lead-zinc waste rock(LZWR)generated from the preconcentration process has attracted substantial attention.A type of dolomitic LZWR with 18 wt.%MgO,27 wt.%CaO,0.29 wt.%Zn and 1.43 wt.%S was used as a replacement flux in the iron ore sintering process.Traditional sinter pot tests were carried out based on an industrial ore blend.The results show that replacing 0%-60%of dolomite with LZWR does not adversely affect the sintering productivity,fuel consumption rate,and the quality of the sinter products,while the Zn and S elements contained in LZWR can be effectively removed with the residual Zn and S contents of the resultant sinter products being less than 0.02 and 0.055 wt.%,respectively.However,substituting LZWR for dolomite as a flux inevitably increases the SO_(2) concentration in the sintering flue gas due to its high sulfur content.Considering the processing capacity of the sintering flue gas desulfurization system,the replacement ratio of dolomite can reach 40%,equal to LZWR consumption of 24.3 kg per ton of sinter.The SO_(2) in sintering flue gas can be recovered to produce(NH_(4))_(2)SO_(4) or HSO_(4),while the volatilized Zn collected into the zinc-containing dust can be subsequently recycled by the rotary hearth furnace process.Therefore,it is technologically and economically feasible to use the LZWR as a replacement flux in the iron ore sintering process,providing a new way for the safe,large-scale and low-cost treatment of LZWR.展开更多
基金supported by the National Natural Science Foundation of China (Nos.40472015, 40802001, and 41372121)the State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation at CDUT (PL200801)
文摘The Upper Permian Changxing dolomite reservoirs serves as one of the most important gas and oil reservoirs in the NE Sichuan Basin. Determining the dolomitizing fluid＇s pathway is regarded as the key to solve the ＂dolomite problem＂ and further petroleum exploration. Outcrop samples from Upper Permian Changhsingian Panlongdong Section were studied using oxygen isotopic analysis, cathodoluminescence（CL） and major element analysis, in an attempt to determine the migration path way and properties of the dolomitizing fluid. Of the Changxing dolomite, the δ18O values ranged from-3.494‰ to-5.481‰, which decreased from the top layer to the bottom in the section; the MgO contents varied from 9.24% to 21.43%, CaO contents from 28.65% to 39.87%, the CaO/MgO ratio from 1.40 to 4.31 and the Mn O contents from 0.004% to 0.009 8%. The Mg O contents showed a downwardly decreasing trend in the section, while the Ca O/Mg O showed an opposite rule. All of the dolomites looked dull or dark when they were exposed to the electron beam of the cathodoluminescence device. None of the fine-to medium grained dolomite showed a banded structure. Given that dolomitizing fluid＇s salinity decreased during the dolomitization process in its pathway, we concluded that the dolomitizing fluid migrated downwardly in Changxing Formation after excluding the possibility of deep burial or meteoric-marine mixing-water influences. As the dolomitizing fluid＇s pathway has always been difficult to be determined in highly dolomitized Formation, this study showed an important application of oxygen isotope values in resolving this problem.
基金financially supported by the National Natural Science Foundation of China(Nos.42372162,U22B6004)the Scientific Research and Technology Development Program of CNPC(Nos.2021DJ0102,2021DJ1808)。
文摘Lacustrine dolomite is paid increasing attention to uncover the diagenetic water condition of paleo-lake and“dolomite problem”.Here,a dolomite nodule from the Qingshankou Formation in the Songliao Basin was analyzed to explore the salinity,alkalinity,and redox conditions of the diagenetic water.Multiple proxies,including bulk boron(B)content,B isotope composition(δ^(11)B_(bul)),boron to gallium weight ratio(B/Ga)and carbonate oxygen isotope composition(δ^(18)O_(carb)),were used to determine the diagenetic water to be brackish-fresh.Through numerical simulation,we calculated the B contents,δ^(11)B values and B/Ga in detritus(e.g.,clay,quartz and feldspar)and dolomite as two endmembers,confirming the intense interference of clay minerals onδ^(11)B_(bul).By using the fittedδ^(11)B of dolomite endmember(20.6‰),we calculated the p H value of the diagenetic water to be 8.2.The negativeδ^(11)B value of detritus endmember(-12.9‰)might be related to the terrestrial weathering.The indicative nature of strontium to barium weight ratio(Sr/Ba)was discussed to deny its applicability as a proxy of salinity in carbonate system.High Sr/Ba ratio in this dolomite nodule indicates a sulfate-poor water condition,consistent with the iron-manganese(Fe-Mn)reduction environments reflected by the Mn/Fe molar ratio.The positive carbonate carbon isotopes(δ^(13)C_(carb),4.5‰-9.4‰)indicate that methanogenesis dominated the formation of dolomite,coinciding with the weak sulfate reduction reaction in sulfate-poor water.The growth of dolomite nodule might be related to the microbial activities of methanogen and iron reducing bacteria,which had not only maintained the salinity,p H,and redox status of the diagenetic water,but also led to a ferricmethane transition zone(FMTZ).This research depicts a scenario about the diagenetic water environment of lacustrine dolomite formed in brackish-fresh water,which is different from that occurred in sulfate-rich condition.
基金Project(BGRIMM-KJSKL-2024-07) supported by the Open Foundation of State Key Laboratory of Mineral Processing,ChinaProjects(52374259,52174239) supported by the National Natural Science Foundation of China。
文摘Surface pretreatment can change the surface properties of minerals,placing them in either a favorable or an unfavorable state for flotation.To solve the separation problem associated with magnesite and dolomite,surface pretreatment experiments with citric acid,tartaric acid,and tannic acid(TA)on magnesite and dolomite as well as flotation experiments on pretreated samples were performed in this study.Experimental results demonstrated that when citric acid and tartaric acid are used for surface pretreatment,the separation effect of magnesite and dolomite is poor.However,when TA is used,the separation effect of magnesite and dolomite improves.SEM and BET analysis indicated that surface pretreatment with TA changes the surface morphology of the two minerals,resulting in additional concave pores on the dolomite surface,and a significant increase in pore size and specific surface area.The adsorption quantity test and contact angle measurement demonstrated that after surface pretreatment with TA,the magnesite adsorption capacity on sodium oleate(NaOL)slightly decreases and the dolomite adsorption capacity on NaOL considerably decreases.XPS detection concluded that the surface pretreatment of TA on the magnesite surface mainly relies on physical adsorption with weak adsorption ability and poor ability to act on Mg sites.The TA surface pretreatment action on the dolomite surface is mainly through chemical adsorption,and it is strongly and selectively adsorbed on the Ca site of dolomite through O.Actual ore rough selection experiments reveal that TA pretreatment successfully removes dolomite from magnesite,resulting in a high-quality magnesite concentrate characterized by a MgO grade of 45.49%and a CaO grade of 0.75%.
基金funded by the National Key Research and Development Program of China(Nos.2022YFF0801202,2022YFF0801200)。
文摘The effect of depositional facies and diagenesis on the reservoir potential of the Sakesar limestone has been assessed through core plug porosity and permeability data,scanning electron microscope(SEM),and petrographic study in three stratigraphic sections(Karuli,Badshah Pur,and Sardhai)of Central Salt Range.Field observations reveal three lithofacies:thin-bedded limestone with shale intercalation,thick-bedded nodular limestone,and highly fractured limestone.Based on a petrographic study,six microfacies have been identified:bioclastic mudstone facies(SKF-1),Lockhartia-nummulitic wackestone facies(SKF-2),Assilina-Alveolina packstone facies(SKF-3),Lockhartia-nummulitic packstone facies(SKF-4),Alveolina grainstone facies(SKF-5),and nummulitic grainstone facies(SKF-6).The Sakesar limestone shows various diagenetic changes such as compaction,dissolution,dolomitization,cementation,and fracturing,resulting in different types of pores.Two reservoir zones are identified in the Sakesar limestone:a mud-dominated reservoir in an outer ramp setting with interparticle and micropores and a bioclastic grain-dominated facies in an inner ramp setting with intraskeletal and fracture porosity.The porosity and permeability of grain-dominated facies(8%-30%and 0.8-8 mD)are higher than mud-dominated facies(4%-15%and 0.5-4 mD)due to intraskeletal/intraparticle pores and dolomitization.
基金Project(IMRI23005)supported by Ordos Science and Technology Bureau,ChinaProjects(52174096,52304110)supported by the National Natural Science Foundation of China。
文摘To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content.The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages:accelerated,decelerated,and stabilized stages.During this process,the number of pores in dolomite increases,while the pore diameter initially decreases and then fluctuates.Microscopic analysis shows that the proportion of mesopores first increases and then decreases,while micropores exhibit the opposite trend,and the proportion of macropores fluctuates around 0%.A model diagram of structural evolution during water absorption has been developed.Additionally,the softening process of dolomite’s water absorption strength is categorized into three stages:a relatively stable stage,an accelerated softening stage dominated by mesopore water absorption,and a decelerated softening stage characterized by micropore water absorption.A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion,and experimental validation indicates its strong applicability.
基金financially supported by the Science Foundation of China University of Petroleum,Beijing(Nos.2462018YJRC030 and 2462020YXZZ020)the China Sponsorship Council(No.202306440071)。
文摘The widespread dolomite of the Sinian Dengying Formation in the Sichuan Basin(China)serves as one of the most important oil and gas reservoir rocks of the basin.Well WT1,as an exploration well,is recently drilled in the Kaijiang County,northeastern Sichuan Basin(SW China),and it drills through the Dengying Formation dolomite at the depth interval of 7500–7580 m.In this study,samples are systematically collected from the cores of that interval,followed by new analyses of carbon-oxygen isotope,major elements,trace elements,rare earth elements(REEs)and EP-MA.The Dengying Formation dolomites of Well WT1 haveδ13C values of 0.37‰to 2.91‰andδ18O values of-5.72‰to-2.73‰,indicating that the dolomitization fluid is derived from contemporary seawater in the near-surface environment,rather than the burial environment.Based on the REE patterns of EPMA-based in-situ data,we recognized the seawater-sourced components,the mixedsourced components and the terrigenous-sourced components,indicating the marine origin of the dolomite with detrital contamination and diagenetic alteration.Moreover,high Al,Th,and Zr contents indicate significant detrital contamination derived from clay and quartz minerals,and high Sr/Ba and Sr/Cu ratios imply a relatively dry depositional environment with extremely high seawater salinity,intensive evaporation,and strong influences of terrigenous sediment.
基金funded by Ordos Science and Technology Plan (Grant No. TD20240003)the National Natural Science Foundation of China (52174096, 52304110)+1 种基金Ordos Science and Technology Bureau (Grant No. IMRI23005)Ordos Science and Technology Plan (Grant No. YF20240021)
文摘Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tunnel of the Yunnan Dianzhong Water Diversion Project,using a combined experimental and modeling approach for systematic analysis.Triaxial cyclic loading-unloading tests were first conducted on dolomite samples soaked in sulfuric acid solutions of varying concentrations,with synchronous monitoring of their mechanical responses(e.g.,peak strength,deformation modulus,porosity changes).These tests,combined with observations of macroscopic morphology and mass changes during soaking,revealed a four-stage degradation pattern of dolomite in sulfuric acid:water absorption,dynamic equilibrium,dissolution,and stabilization.Key quantitative relationships established that as sulfuric acid concentration increased(from 0%to 15%),the peak strength of dolomite decreased significantly(by 7.49%to 24.99%),while porosity markedly increased(by 45%to 130%).Further post-failure analysis(fracture surface observation)and scanning electron microscopy(SEM)micro-characterization uncovered the intrinsic mechanisms of acid-induced damage:the acid solution not only promoted macroscopic crack propagation and increased fracture surface roughness but also triggered severe structural deterioration at the microscale,including enlarged crystal spacing,dissolution of gel-like substances,formation of intra-crystalline pores,weakened interparticle cementation,and development of macropores.The extent of this deterioration was positively correlated with acid concentration.Based on the experimentally revealed chemo-mechanical coupling damage mechanism between acid and rock,this study established,for the first time,a multi-scale predictive model capable of quantitatively correlating acid concentration,microstructural deterioration,and degradation of macroscopic mechanical properties.The development of this model not only deepens the quantitative understanding of the dolomite sanding mechanism but also provides a crucial theoretical tool for assessing surrounding rock stability and predicting risks in similar water diversion tunnel engineering.Addressing the specific risks of water and H^(+) erosion in the Xiaopu Tunnel,the research findings directly informed the engineering reinforcement strategy:concrete lining is recommended as the primary load-bearing structure,supplemented by surrounding rock surface protection measures,to effectively mitigate the acid-induced damage process and enhance the long-term stability of the surrounding rock.
基金The National Natural Science Foundation of China under contract Nos 42330810 and U19B6003-01the China National Petroleum Corporation Science Research and Technology Development Project under contract Nos 2021DJ1501 and 2024DQ03016.
文摘The dominant lithofacies of reservoirs in the Barra Velha formation of the study area are grainstones,which exhibit strong heterogeneity,and the seismic responses of buildups are characterized by low relief,posing a substantial challenge in evaluating the factors controlling high-quality reservoir development.This study thoroughly investigated sedimentary facies and diagenetic processes based on petrological and geophysical data,and a semi-open-rimmed carbonate platform model was established to illustrate the lithofacies distribution pattern.Additionally,the diagenetic processes and their main controlling factors were analyzed,and an attempt was made to establish a diagenetic sequence.Our findings indicate that sedimentary processes control the distribution of lithofacies,while diagenesis ultimately determines the petrophysical properties.The lithofacies types are closely associated with depositional environments.Shrub-like stromatolites are more developed at the bench margin and inner slope,while spherulites occur preferentially in the bench interior and mid-slope environments.Laminites accumulate in profundal or bench interior facies,whereas grainstones are present across all depositional environments,although their components vary.Integrated seismic attributes revealed that the bench margin exhibits nearly circular features,representing favorable conditions for high-quality reservoir development.The primary diagenetic processes in the study area include meteoric diagenesis,chemical compaction,and possible hydrothermal activity.During the eodiagenetic phase,the dissolution of Mg-clays played a key role in the diagenesis of carbonate rocks in the Barra Velha formation.This process typically occurred at structural highs,where Mg-clays were replaced by calcite spherulites,silicates,and dolomite.Some grainstones developed dolomite rims around particles,enhancing their resistance to compaction and preserving primary porosity.In the mesodiagenetic phase,chemical compaction and hydrothermal activity often caused primary pores to be filled with mosaic or blocky calcite and macrocrystalline quartz,leading to reduced permeability and porosity.Although dissolution was common in the study area,its impact on increasing pore space was limited.This study aims to improve drilling success rates in high-quality reservoirs and enhance hydrocarbon discoveries in the study area while also contributing to a better understanding of the evolution and distribution of high-quality reservoirs in analogous lacustrine carbonate settings.
基金supported by Guizhou Provincial Science and Technology Projects(No.ZK[2021]ordinary 199)the National Natural Science Foundation of China(Nos.42262019,92062221)the National Key R&D Program of China(No.2017YFC0603103)。
文摘The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin(NW China)was mainly deposited in a shallow platform,which was intensely bioturbated with burrows filled with both dolomites and calcites.This study aims to figure out the controls on the dolomitization of burrow infills and the effects on petroleum reservoir quality based on petrographic examination,fluid inclusion microthermometry,and isotopic(C-O-Sr)geochemical analyses.The differentiation of burrow-associated carbonates(dolomites and calcites)was likely controlled by the interactions of sea-level oscillations of variable orders and depositional environments.The burrow-associated dolomites(BADs)were precipitated in a relatively restricted(i.e.,lagoon)depositional environment during the lowstand of long-term sea level.In contrast,the burrow-associated calcites(BACs)were formed in a water circulation-improved lagoonal environment during the transgression of long-term sea level.Isotopic geochemical data indicate that the BADs in the Yingshan Formation were formed from slightly saline(i.e.,mesosaline to penesaline)seawater,whereas the BACs were precipitated from nearly normal seawater.In addition to the anoxic condition,the presence of marine-sourced organic matter and sulfate-reducing bacteria,and a sufficient supply of dolomitizing fluids enriched in magnesium ions(Mg^(2+))and their Mg^(2+)concentration may have played a critical role in the formation of BADs.In the more permeable and disturbed burrow sediments as a result of burrowing,penetrating fluids with higher salinities and higher Mg^(2+)concentration relative to seawater favored dolomite precipitation.The fluids with seawater-like Mg^(2+)concentration,however,would lead to calcite precipitation.The progressive dolomitization of these burrowed sediments could have propagated the dolomitizing fronts and extended into ambient limestones,leading to the development of extensive dolomites.This dolomitization process can improve the petrophysical properties(porosity and permeability)and the potential as hydrocarbon reservoirs during the emplacement of hydrocarbons from underlying source rocks of the Cambrian to Lower Ordovician.
基金The research project is funded by the Geological Joint Fund(U2244209).
文摘The Majiagou Formation in the Fuxian area of the southeastern Ordos Basin has undergone a complex diagenetic evolution history under the influence of eustacy and the Caledonian karstification,resulting in several complex reservoir types.Through analyses of mineralogy,petrology,and reservoir geology,three major types of dolomite reservoirs with different genetic mechanisms,including anhydritic moldicdissolved pore type,dolomitic intercrystalline-pore type,and fractured type were identified,and their formation mechanisms and distribution patterns were examined.The aphanocrystalline to very finecrystalline anhydritic dolomite was resulted from Sabhak dolomitization,and is characterized by small size of crystals and high content of anhydrite.Dolomite reservoirs of anhydritic moldic-dissolved pore type were developed in multi-stage dissolution processes and mainly distributed at higher positions of the paleogeomorphology where the filling was weak.The very fine to fine-crystalline dolomite of shoal facies was formed under seepage-reflux dolomitization,and characterized by larger sizes of crystals and well-developed intercrystalline pores.Dolomite reservoirs of intercrystalline-pore type were mainly developed at the lower positions of the paleogeomorphology where bedding-parallel karst dissolution was strong.The fractured dolomite reservoirs,generated by the anhydrite swelling and karst cave collapse,occur in multiple horizons but within limited areas due to multi-stage fillings.
文摘The origin of dolostone in the Middle Jurassic Buqu Formation of the Plateau Basin has been a subject of prolonged debate.This study combines detailed petrological observations with analyses of Mg-C-O isotopes and elements to constrain the origin of dolostones in the Buqu Formation.Petrography and cathodoluminescence(CL)examination identified three types of matrix dolostones:very finely to finely crystalline dolostone(D1),finely to medium crystalline dolostone(D2),and medium to coarsely crystalline dolostone(D3).The analysis of the diagenesis sequence reveals that D1 originated from the dolomitization of grainstone in the early diagenetic phase,whereas D2 and D3 resulted from the recrystallization of D1 during the later burial phase.The presence of high Na(>100 ppm),low Fe(<1000 ppm),low Mn(<250 ppm),positive Ce anomaly,LREE enrichment,stableδ^(26)Mg(-2.28‰to-2.04‰),andδ^(13)C(1.02‰-2.95‰)indicates that the early dolomitization fluid was oxidized seawater.As the crystal size increases(D1→D2→D3),the progressively rising Mn content and significantly negativeδ^(18)O(-10.72‰to-7.81‰)suggest that the dolostone has experienced modification and alteration by buried pore water in the later stages.The fluctuations in relative sea level during the sedimentary deposition of the Buqu Formation were reconstructed through the utilization of Na,Sr/Cu,Sr/Ba,Rb/Sr,∑REE,andδ^(13)C.It was observed that theδ^(26)Mg of dolostone closely mirrored the variations in sea level.The consistent trend of change confirms that sea level fluctuations control the formation and distribution of early dolostone.Frequent sea level rise and fall prompted the limestone deposited on the carbonate platform to be continuously transformed into dolostone,which accumulates over a long period to form large-scale thick dolostone.After the formation entered the burial stage,under the combined action of high Mg/Ca ratio pore water,high temperature,and high pressure,the early dolostone experienced the adjustment of burial dolomitization.This research offers a typical case study on the application of Mg-C-O isotope and elements to determine the origin of dolostone.This will aid in a more comprehensive understanding of the formation process of dolostone in ancient rock records.
基金Supported by the National Natural Science Foundation of China(42172166)National Natural Science Foundation and CNPC Joint Fund Project(U23B20154)CNPC-Southwest Petroleum University Science and Technology Cooperation Project(2020CX010000).
文摘This paper discusses the characteristics and formation mechanism of thin dolomite reservoirs in the lower submember of the second member of the Permian Maokou Formation(lower Mao 2 Member)in the Wusheng-Tongnan area of the Sichuan Basin,SW China,through comprehensive analysis of geological,geophysical and geochemical data.The reservoir rocks of the lower Mao 2 Member are dominated by porphyritic vuggy dolomite and calcareous dolomite or dolomitic limestone,which have typical karst characteristics of early diagenetic stage.The dolomites at the edge of the karst system and in the fillings have dissolved estuaries,and the dolomite breccia has micrite envelope and rim cement at the edge,indicating that dolomitization is earlier than the early diagenetic karstification.The shoal facies laminated dolomite is primarily formed by the seepage reflux dolomitization of moderate-salinity seawater.The key factors of reservoir formation are the bioclastic shoal deposition superimposed with seepgae reflux dolomitization and the karstification of early diagenetic stage,which are locally reformed by fractures and hydrothermal processes.The development of dolomite vuggy reservoir is closely related to the upward-shallowing sequence,and mainly occurs in the late highstand of the fourth-order cycle.Moreover,the size of dolomite is closely related to formation thickness,and it is concentrated in the formation thickness conversion area,followed by the thinner area.According to the understanding of insufficient accommodation space in the geomorphic highland and the migration of granular shoal to geomorphic lowland in the late highstand of the third-order cycle,it is proposed that the large-scale shoal-controlled dolomite reservoirs are distributed along structural highs and slopes,and the reservoir-forming model with shoal,dolomitization and karstification jointly controlled by the microgeomorphy and sea-level fluctuation in the sedimentary period is established.On this basis,the paleogeomorphology in the lower Mao 2 Member is restored using well-seismic data,and the reservoir distribution is predicted.The prediction results have been verified by the latest results of exploration wells and tests,which provide an important reference for the prediction of thin dolomite reservoirs under similar geological setting.
基金supported by the National Natural Science Foundation of China(Grant No.42162026)the Basic Research Program in Yunnan Province,China(Grant No.202401AT070328)the Young Talents Project of“Xingdian Talent Support Program"in Yunnan Province,China(Grant No.YNWR-QNBJ-2020-019).
文摘Disintegrated dolomite slope and tunnel disasters occur frequently due to poor water stability of disintegrated dolomite,primarily in a form of seepage failure.For engineering purposes,it is critical to determine the seepage properties of disintegrated dolomite within the strata.However,conventional experimental methods are time-consuming and expensive and may not be effective in investigating seepage characteristics due to the heterogeneity of disintegrated dolomite.In this study,pore network model(PNM)was established by the computerized tomography(CT)scanning technology to characterize the pores.Meanwhile,the seepage and coefficient of permeability under different inlet stress conditions based on the accurate pore model were realized by linking the commercial image processing software Avizo with the commercial multi-physics modeling package Comsol.The results show that the porosities of severely and completely disintegrated dolomites are 29.17% and 45.37%,respectively.The grade of pore development increases with disintegration grade,which facilitates seepage failure.Severely and completely disintegrated dolomites have the coefficients of permeability of 9.67×10^(-7) m/s and 1.61×10^(-6) m/s,respectively.Under conventional conditions,severely and completely disintegrated dolomites undergo seepage failure above a pressure difference of 6×10^(3) Pa and 5×10^(3) Pa,respectively.These results are consistent with both in situ water pressure tests in the borehole and laboratory tests with the constant-head method,demonstrating that CT scanning is an effective method for observing fractures and pores in disintegrated dolomite for seepage evaluation.
基金supported by National Natural Science Foundation of China(Grant Nos. 40839908 and 40672072)the Research Fund for the Doctoral Program of Higher Education of China (Grant No.20050616005)
文摘The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years.Because of the dolomite-hosted reservoirs in the Feixianguan Formation,these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists.Based on the homogenization temperatures of fluid inclusions,oxygen isotopic composition and their calculated temperatures,and the burial and thermal history of the typical well,it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation,Northeastern Sichuan Basin.Only a minority of dolomites are formed by high-temperature dolomitizing fluids.The ending depth interval of low-temperature dolomitizing fluids was about 1000-2500 m,of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic.The main depth interval of high-temperature dolomitizing fluids was about 3200-4500 m,of which the correspondingly main timing interval was approximately early-middle Middle Jurassic.The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation,Northeastern Sichuan Basin.
基金Supported by the National Natural Science Foundation of China(U22B6002)National Project for Oil and Gas Technology(2016ZX05-004)CNPC Science and Technology Project(2023ZZ02).
文摘The Ediacaran–Ordovician strata within three major marine basins(Tarim,Sichuan,and Ordos)in China are analyzed.Based on previous studies focusing on the characteristics of the Neoproterozoic–Cambrian strata within the three major basins(East Siberian,Oman,and Officer in Australia)overseas,the carbonate–evaporite assemblages in the target interval are divided into three types:intercalated carbonate and gypsum salt,interbedded carbonate and gypsum salt,and coexisted carbonate,gypsum salt and clastic rock.Moreover,the concept and definition of the carbonate-evaporite assemblage are clarified.The results indicate that the oil and gas in the carbonate-evaporite assemblage are originated from two types of source rocks:shale and argillaceous carbonate,and confirmed the capability of gypsum salt in the saline environment to drive the source rock hydrocarbon generation.The dolomite reservoirs are classified in two types:gypseous dolomite flat,and grain shoalµbial mound.This study clarifies that the penecontemporaneous or epigenic leaching of atmospheric fresh water mainly controlled the large-scale development of reservoirs.Afterwards,burial dissolution transformed and reworked the reservoirs.The hydrocarbon accumulation in carbonate-evaporite assemblage can be categorized into eight sub-models under three models(sub-evaporite hydrocarbon accumulation,supra-evaporite hydrocarbon accumulation,and inter-evaporite hydrocarbon accumulation).As a result,the Cambrian strata in the Tazhong Uplift North Slope,Maigaiti Slope and Mazatag Front Uplift Zone of the Tarim Basin,the Cambrian strata in the eastern-southern area of the Sichuan Basin,and the inter-evaporite Ma-4 Member of Ordovician in the Ordos Basin,China,are defined as favorable targets for future exploration.
基金supported by the National Natural Science Foundation of China (Nos.51974064,52174239,and 52374259)the Open Project of the Key Laboratory of Solid Waste Treatment and Resource Utiliza-tion of the Ministry of Education,China (No.23kfgk02).
文摘Flotation separation of magnesite and its calcium-containing carbonate minerals is a difficult problem.Recently,new regulat-ors have been proposed for magnesite flotation decalcification,although traditional regulators such as tannin,water glass,sodium carbon-ate,and sodium hexametaphosphate are more widely used in industry.However,they are rarely used as the main regulators in research because they perform poorly in magnesite and dolomite single-mineral flotation tests.Inspired by the limonite presedimentation method and the addition of a regulator to magnesite slurry mixing,we used a tannin pretreatment method for separating magnesite and dolomite.Microflotation experiments confirmed that the tannin pretreatment method selectively and largely reduces the flotation recovery rate of dolomite without affecting the flotation recovery rate of magnesite.Moreover,the contact angles of the tannin-pretreated magnesite and dolomite increased and decreased,respectively,in the presence of NaOl.Zeta potential and Fourier transform infrared analyses showed that the tannin pretreatment method efficiently hinders NaOl adsorption on the dolomite surface but does not affect NaOl adsorption on the magnesite surface.X-ray photoelectron spectroscopy and density functional theory calculations confirmed that tannin interacts more strongly with dolomite than with magnesite.
基金Supported by the National Natural Science Foundation of China(42172177)CNPC Scientific Research and Technological Development Project(2021DJ05)PetroChina-Southwest University of Petroleum Innovation Consortium Project(2020CX020000).
文摘Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the controlling factors of reservoir development were analyzed,and the formation model of“intra-platform shoal thin-layer dolomite reservoir”was established.The Qixia Formation is a regressive cycle from bottom to top,in which the first member(Qi1 Member)develops low-energy open sea microfacies,and the second member(Qi2 Member)evolves into intra-platform shoal and inter-shoal sea with decreases in sea level.The intra-platform shoal is mainly distributed near the top of two secondary shallowing cycles of the Qi2 Member.The most important reservoir rock of the Qixia Formation is thin-layer fractured-vuggy dolomite,followed by vuggy dolomite.The semi-filled saddle dolomite is common in fracture-vug,and intercrystalline pores and residual dissolution pores combined with fractures to form the effective pore-fracture network.Based on the coupling analysis of sedimentary and diagenesis characteristics,the reservoir formation model of“pre-depositional micro-paleogeomorphology controlling shoal,sedimentary shoal controlling dolomite,penecontemporaneous dolomite benefiting preservation of pores,and late hydrothermal action effectively improving reservoir quality”was systematically established.The“first-order high zone”micro-paleogeomorphology before the deposition of the Qixia Formation controlled the development of large area of intra-platform shoals in Gaoshiti area during the deposition of the Qi2 Member.Shoal facies is the basic condition of early dolomitization,and the distribution range of intra-platform shoal and dolomite reservoir is highly consistent.The grain limestone of shoal facies is transformed by two stages of dolomitization.The penecontemporaneous dolomitization is conducive to the preservation of primary pores and secondary dissolved pores.The burial hydrothermal fluid enters the early dolomite body along the fractures associated with the Emeishan basalt event,makes it recrystallized into medium–coarse crystal dolomite.With the intercrystalline pores and the residual vugs after the hydrothermal dissolution along the fractures,the high-quality intra-platform shoal-type thin-layer dolomite reservoirs are formed.The establishment of this reservoir formation model can provide important theoretical support for the sustainable development of Permian gas reservoirs in the Sichuan Basin.
基金Supported by the National Science and Technology Major Project(2016ZX05007004-001)Innovation Fund Project of CNPC Carbonate Rock Key Laboratory(RIPED-HZDZY-2019-JS-695).
文摘To analyze the episodic alteration of Middle Permian carbonate reservoirs by complex hydrothermal fluid in southwestern Sichuan Basin,petrology,geochemistry,fluid inclusion and U-Pb dating researches are conducted.The fractures and vugs of Middle Permian Qixia–Maokou formations are filled with multi-stage medium-coarse saddle dolomites and associated hydrothermal minerals,which indicates that the early limestone/dolomite episodic alteration was caused by the large-scale,high-temperature,deep magnesium-rich brine along flowing channels such as basement faults or associated fractures under the tectonic compression and napping during the Indosinian.The time of magnesium-rich hydrothermal activity was from the Middle Triassic to the Late Triassic.The siliceous and calcite fillings were triggered by hydrothermal alteration in the Middle and Late Yanshanian Movement and Himalayan Movement.Hydrothermal dolomitization is controlled by fault,hydrothermal property,flowing channel and surrounding rock lithology,which occur as equilibrium effect of porosity and permeability.The thick massive grainstone/dolomites were mainly altered by modification such as hydrothermal dolomitization/recrystallization,brecciation and fracture-vugs filling.Early thin-medium packstones were mainly altered by dissolution and infilling of fracturing,bedding dolomitization,dissolution and associated mineral fillings.The dissolved vugs and fractures are the main reservoir space under hydrothermal conditions,and the connection of dissolved vugs and network fractures is favorable for forming high-quality dolomite reservoir.Hydrothermal dolomite reservoirs are developed within a range of 1 km near faults,with a thickness of 30–60 m.Hydrothermal dolomite reservoirs with local connected pore/vugs and fractures have exploration potential.
基金supported by the Fundamental Research Funds for the Central Universities(No.N2201005).
文摘Given the depletion of high-quality magnesite deposits and the rising demand for high-end magnesium materials,the separation and utilization of high-calcium magnesite ores have become essential.However,the similar surface properties and solubility of semi-soluble salt-type minerals,pose significant challenges for the utilization of dolomite-rich magnesite resources.In this study,1-hydroxypropane-1,1-di phosphonic acid(HPDP)was identified for the first time as a high-performance depressant for dolomite.Various tests,including contact angle measurements,ζ potential analysis,X-ray photoelectron spectroscopy,and atomic force microscopy,were conducted to elucidate the interfacial interaction mechanisms of HPDP on the surfaces of the two minerals at different scales.Additionally,molecular modeling calculations were used to detail the spatial matching relationship between HPDP and the crystal faces of the two minerals.It was emphasized that HPDP specifically adsorbed onto the dolomite surface by forming calcium phosphonate,ensuring that the dolomite surface remained hydrophilic and sank.Moreover,it was found that the adsorption strength of HPDP on the mineral surfaces depended on the activity of the metal sites and their spatial distribution.These findings provide a theoretical foundation for the molecular design of flotation reagents for high-calcium magnesite ores.
基金This work was supported by the National Natural Science Foundation of China(Grant Number 52004339)Hunan Provincial Key Research and Development Project(Grant Number 2022SK2075).
文摘With increasingly stringent environmental protection policies,cost-effective and value-added treatment of massive lead-zinc waste rock(LZWR)generated from the preconcentration process has attracted substantial attention.A type of dolomitic LZWR with 18 wt.%MgO,27 wt.%CaO,0.29 wt.%Zn and 1.43 wt.%S was used as a replacement flux in the iron ore sintering process.Traditional sinter pot tests were carried out based on an industrial ore blend.The results show that replacing 0%-60%of dolomite with LZWR does not adversely affect the sintering productivity,fuel consumption rate,and the quality of the sinter products,while the Zn and S elements contained in LZWR can be effectively removed with the residual Zn and S contents of the resultant sinter products being less than 0.02 and 0.055 wt.%,respectively.However,substituting LZWR for dolomite as a flux inevitably increases the SO_(2) concentration in the sintering flue gas due to its high sulfur content.Considering the processing capacity of the sintering flue gas desulfurization system,the replacement ratio of dolomite can reach 40%,equal to LZWR consumption of 24.3 kg per ton of sinter.The SO_(2) in sintering flue gas can be recovered to produce(NH_(4))_(2)SO_(4) or HSO_(4),while the volatilized Zn collected into the zinc-containing dust can be subsequently recycled by the rotary hearth furnace process.Therefore,it is technologically and economically feasible to use the LZWR as a replacement flux in the iron ore sintering process,providing a new way for the safe,large-scale and low-cost treatment of LZWR.
